The present invention relates to rotating compensator ellipsometer systems, and more particularly to spectroscopic rotating compensator ellipsometer systems which comprise spatial filters before and/or after an investigated sample system.
Not limited to, but particularly in the case where an electromagnetic beam is utilized to investigate a sample system which presents with a varying depth surface topology, it is important to provide an electromagnetic beam of a known lateral dimension and which presents with a relatively simple cross-sectional intensity profile.
It is noted that often electromagnetic beams present with a substantially arbitrary intensity profile, with the highest intensity being located centrally, which intensity generally decreasing as with increasing radius. While an arbitrary beam intensity profile is typically acceptable for use in ellipsometry and related practices, it has been found that once the intensity of a substantially arbitrary profile beam of electromagnetic radiation has decreased to, as an arbitrary example, say 10% of its peak, it does not always continue to decay directly to essentially zero (0.0). Instead, it often presents irregularly as a function of radius, (eg. easily visualized as being generally similar to the Fourier transform of a square wave), and such irregular intensity content can adversely affect ellipsometer performance. The cause of said irregular intensity profile can include such as optical element wavelength dependent diffraction, surface roughness or other non-idealities, and where electromagnetic radiation is provided via an aperture or via the end of a light fiber contained in a cladding, electromagnetic radiation falling outside a geometric image thereof is often of an irregular intensity content.
It would be of benefit, as regards obtaining accurate data from application of ellipsometers and the like systems, if the intensity of an electromagnetic beam could be forced to decay quickly to zero (0.0), rather than demonstrate an irregular intensity profile as a function of radius in an outer annulus region.
With an eye to the present invention, a Search of Patents was conducted. Perhaps the most relevant Patent identified is U.S. Pat. No. 5,517,312 to Finarov. Said 312 Patent describes application of a scattered light reducing system at the entry to a Detector in a Rotating Analyzer or Rotating Polarizer Ellipsometer System, which scattered light reducing system consists of two lenses with a pin-hole containing diaphram located midway therebetween, and at the focal lengths of said lenses. Said scattered light reducing system is present after a sample system and processes electromagnetic radiation after it interacts with said sample system. The pinhole is described as serving to reduce scattered light and providing high spatial resolution. Another Patent identified is that to Campbell et al., U.S. Pat. No. 5,148,323. Said 323 Patent describes a Spatial Filter in which a pinhole is located other than at the focal length of a converging lens. U.S. Pat. No. 3,905,675 to McCraken describes a Spatial Filter containing system which enables observation of a weak source of electromagnetic radiation in the presence of strong sources thereof. U.S. Pat. No. 5,684,642 to Zumoto et al., describes an optical transmission system for use in fashioning an electromagnetic beam for use in machining materials which combines a Spatial Filter and an Optical Fiber. U.S. Pat. No. 4,877,960 to Messerschmidt et al. is identified as it describes masking energy from outside the target area in a microscope having dual remote image masking.
Continuing, Spectroscopic Rotating Compensator Ellipsometer Systems are also known in the art. And, as mentioned, application a Spatial Filters near a Detector, in the context of Rotating Polarizer and Rotating Analyzer Ellipsometer Systems has been reported, (see U.S. Pat. No. 5,517,312 to to Finerov). However, the application of Spatial Filters in Rotating Compensator Ellipsometer Systems, such as the Rotating Compensator Ellipsometer System Claimed in co-owned U.S. Pat. No. 5,872,630, has not here-to-fore been known. Said 630 Patent, which is incorporated by reference hereinto and which is co-owned with this Application, is disclosed as it describes an ellipsometer system in which an analyzer and polarizer are maintained in a fixed in position during data acquisition, while at least one compensator is caused to continuously rotate.
A Patent to Dill et al., U.S. Pat. No. 4,053,232 is disclosed as it describes a Rotating-Compensator Ellipsometer System which operates utilizing monochromatic light.
A Patent to Aspnes et al., U.S. Pat. No. 5,877,859 is disclosed as it describes a Broadband Spectroscopic Rotating Compensator Ellipsometer System wherein the Utility is derived from selecting a wavelength range and compensator so that at least one wavelength in said wavelength range has a retardation imposed of between 135 and 225 degrees, and another wavelength in said wavelength range has a retardation imposed which is outside that retardation range.
A Patent, U.S. Pat. No. 5,329,357 to Bernoux et al. is also identified as it Claims use of fiber optics to carry electromagnetic radiation to and from an ellipsometer system which has at least one polarizer or analyzer which rotates during data acquisition. It is noted that if both the polarizer and analyzer are stationary during data acquisition that this Patent is not controlling where electromagnetic radiation carrying fiber optics are present.
Further Patents of general interest of which the Inventors are aware include those to Woollam et al, U.S. Pat. No. 5,373,359, Patent to Johs et al. U.S. Pat. No. 5,666,201 and Patent to Green et al., U.S. Pat. No. 5,521,706, and Patent to Johs et al., U.S. Pat. No. 5,504,582 are disclosed for general information as they pertain to ellipsometer systems.
A Patent to He et al., U.S. Pat. No. 5,963,327 is also disclosed as it describes a laterally compact ellipsometer system which enables providing a polarized beam of electromagnetic radiation at an oblique angle-of-incidence to a sample system in a small spot area.
In addition to the identified Patents, certain Scientific papers are also identified.
A paper by Johs, titled xe2x80x9cRegression Calibration Method for Rotating Element Ellipsometersxe2x80x9d, Thin Solid Films, 234 (1993) is also disclosed as it describes a mathematical regression based approach to calibrating ellipsometer systems.
A Review paper by Collins, titled xe2x80x9cAutomatic Rotating Element Ellipsometers: Calibration, Operation and Real-Time Applicationsxe2x80x9d, Rev. Sci. Instrum., 61(8) (1990), is identified for general information.
Even in view of the known art, in the context of rotating compensator ellipsometer systems, a need remains for a system and methodology of its use, which adds spatial filter means before and/or after a sample sytem, to, for instance, fashion a beam with a radially essentially arbitrary Profile which directly approaches zero intensity. The present invention meets said need.
Rotating Compensator Ellipsometer Systems provide many benefits, (eg. Sample System PSI and DELTA investigation limiting xe2x80x9cdead-spotsxe2x80x9d are not present), but until a co-owned Patent to Johs et al., U.S. Pat. No. 5,872,630 taught otherwise, it was generally believed that in the absence of essentially Achromatic xe2x80x9cidealxe2x80x9d Compensators, it would be prohibitively difficult and expensive to build, calibrate and utilize a xe2x80x9cSpectroscopicxe2x80x9d Rotating Compensator Ellipsometer System. This is to be understood in light of the fact that Compensators which are essentially Achromatic, (ie. provide essentially constant retardation over a large range of Wavelengths, such as 190-1000 nanometers), are not generally and economically available as off-the-shelf items. The present invention expands on the utility available from the Spectroscopic Rotating Compensator Ellipsometer System previously taught in the 630 Patent. In very general terms the present invention is a rotating compensator ellipsometer system which generates an electromagnetic beam and causes it to impinge upon a sample system, said spectroscopic rotating compensator ellipsometer system comprising, prior to and/or after said sample system, at least one spatial filter which, for instance, serves to attenuate an outer annular region from said electromagnetic beam as it passes therethrough. More specifically, the present invention spectroscopic rotating compensator ellipsometer system is affordable, easy to calibrate and utilize and comprises a Source of a Polychromatic Beam of Electromagnetic Radiation, a Polarizer, a Stage for Supporting a Sample System, an Analyzer, a Dispersive Optics and at least one Photo Array Detector Element System which contains a multiplicity of Detector Elements, which Spectroscopic Rotating Compensator System further comprises at least one Rotatable Compensator(s) positioned at location(s) selected from the group consisting of:
(before said stage for supporting a sample system and after said stage for supporting a sample system and both before and after said stage for supporting a sample system). Said present invention Spectroscopic Rotating Compensator Ellipsometer System also comprises a Spatial Filter System which minimally sequentially comprises:
beam converging at least one lens and/or mirror;
diaphram with a pin hole therein located near the focal length of said beam converging at least one lens and/or mirror; and
beam collimating at least one lens and/or mirror;
such that in use an electromagnetic beam which is caused to interact with said beam converging at least one lens and/or mirror becomes focused on, and at least partially passes through said pin hole in said diaphram, and then becomes recollimated by said second beam at least one collimating lens and/or mirror.
A preferred present invention spectroscopic rotating compensator based ellipsometer system comprises addition of an aperture such that the configuration is:
first beam collimating lens;
aperture;
first beam converging at least one lens and/or mirror;
diaphram with a pin hole therein located essentially at the focal length of said beam converging at least one lens and/or mirror; and
second beam collimating at least one lens and/or mirror;
and such that, in use, the central portion of the electromagnetic beam which is collimated by said first beam collimating lens is caused to pass through said aperture, become focused on and at least partially pass through said pin hole in said diaphram by said first beam converging at least one lens and/or mirror, and become recollimated by said second beam collimating at least one lens and/or mirror.
The present invention can also be considered to be a spectroscopic rotating compensator based ellipsometer system which comprises:
a polarization state generator comprising said Source of a Polychromatic Beam of Electromagnetic Radiation and Polarizer;
means for supporting a sample system; and
a polarization state detector, comprising said Analyzer, a Dispersive Optics and at least one Photo Array Detector Element System which contains a multiplicity of Detector Elements;
with at least one of said polarization state generator and polarization state detector further comprising at least one compensator;
and a spatial filter being present in at least one selection from the group consisting of:
said polarization state generator; and
said polarization state detector;
which spatial filter which sequentially comprises:
first at least one lens and/or mirror;
pin hole containing diaphram; and
second at least one lens and/or mirror;
with the optional inclusion of
collimating lens;
aperture;
prior to said first at least one lens and/or mirror;
said pin hole containing diaphram being positioned near the focal points of said first and second at least one lenses or mirrors, such that a collimated electromagnetic beam enters said first at least one lens or mirror, is converged and at least partially passes through said pin hole, and is recollimated by said second at least one lens and/or mirror. Spatial filter(s) can be present in either the polarization state generator or polarization detector. Said spatial filter can be positioned at a location selected from the group consisting of:
between the source of electromagnetic radiation and the polarizer;
between a compensator and sample system;
between the sample system and a compensator;
between a compensator and analyzer; and
between the analyzer and detector.
The present invention is further, in the context of spectroscopic rotating compensator based ellipsometer systems, a method of processing electromagnetic beams to, for instance, eliminate a radially outer annulus thereof, said outer annulus often being comprised of low intensity level irregular content, said method comprising placing at least one spatial filter(s) such that said electromagnetic beam passes therethrough, each present spatial filter sequentially comprising:
aperture;
beam converging at least one lens and/or mirror;
diaphram with a pin hole therein located near the focal length of said beam converging at least one lens and/or mirror; and
beam collimating at least one lens and/or mirror;
such that, in use, an electromagnetic beam which is caused to pass through said aperture, become focused on and at least partially pass through said pin hole in said diaphram by said beam converging at least one lens and/or mirror, and become recollimated by said second beam collimating at least one lens and/or mirror.
Said present invention method can be recited as, in the context of a spectroscopic rotating compensator ellipsometer system which causes a beam of electromagnetic radiation to interact with a sample system, comprising the steps of:
a. providing a beam of electromagnetic radiation;
b. providing a sample system;
c. placing at least one spatial filter(s) in the pathway of said electromagnetic beam such that said electromagnetic beam passes therethrough prior to or after said electromagnetic beam being caused to interact with a sample system;
the purpose being to, for instance, eliminate a radially outer annulus of said electromagnetic beam which is comprised of a low intensity level irregular content.
In the preferred present invention Rotating Compensator Ellipsometer System, said at least one Compensator(s) utilized in the present invention can be essentially any available, reasonably priced, off-the-shelf Retardation providing system, including non-Achromatic, Berek-type, Zero-Order Waveplate, Multiple-Order Waveplate, Combinations of Multiple-Order Waveplates, Polymer Retarder, Mica Waveplate, Freshnel Rhomb, Achromatic, and Pseudo-Achromatic, etc.
For general information, it is noted that a Berek-type Compensator is a uniaxially anisotropic plate of material in which the Optical Axis is oriented perpendicularly to a plate surface thereof. When a Polarized Beam of Electromagnetic Radiation is caused to be incident other than along the Optical Axis, orthogonal components thereof encounter different effective Indicies of Refraction, thereby effecting retardation therebetween. A Zero-Order Quartz Waveplate is typically constructed by combining two Multi-Order (Quartz) Waveplates which have Optical Axes oriented at ninety (90) degrees with respect to one another. The two Multi-Order waveplates are selected so that the difference in retardation entered by each gives rise to an overall Zero-Order retardance characteristic. Polymer Compensators are made of a polymer material and can provide true Zero-Order retardance which, as do many Compensators, provides an inverse wavelength functional Retardance Characteristic. Essentially Achromatic (Pseudo-Achromatic) Compensators can be constructed by stacking appropriately chosen Polymer and Crystal waveplates. A potential advantage of said essentially Achromatic Compensators is that Retardance can be essentially constant over a range of wavelengths.
While it is known that generally available Compensators do not provide an exact Ninety (90) Degrees of Retardation at all wavelengths over a relatively large range of Wavelengths, the present invention, as described later herein, utilizes a Regression based Calibration procedure which compensates for said non-ideal Compensator Retardation characteristics. And while it is true that the sensitivity and accuracy of a Rotating Compensator System degrades as the Retardance provided by a utilized Compensator approaches zero (0.0) or one-hundred-eighty (180) degrees, it has been found that Compensators which demonstrate Retardation, over a range of utilized Wavelengths, of from forty (40) to one-hundred-seventy (170) degrees, are acceptable for use in the present invention, and allow achieving very impressive results over a demonstrated relatively large range of wavelengths, (eg. at least two-hundred-fifty (250) to one-thousand (1000) nanometers).
When the present invention Spectroscopic Rotating Compensator Ellipsometer System is used to investigate a Sample System present on said Stage for Supporting a Sample System, said Analyzer and Polarizer are maintained essentially fixed in position and at least one of said at least one Compensator(s) is/are caused to continuously rotate while a Polychromatic Beam of Electromagnetic Radiation produced by said Source of a Polychromatic Beam of Electromagnetic Radiation is caused to pass through said Polarizer and said Compensator(s). Said Polychromatic Beam of Electromagnetic Radiation is also caused to interact with said Sample System, pass through said Analyzer and interact with said Dispersive Optics such that a Multiplicity of Essentially Single Wavelengths are caused to simultaneously enter a corresponding multiplicity of Detector Elements in said Detector System Photo Array.
While the present invention can utilize essentially any Compensator, a preferred embodiment of the present invention provides that at least one of said at least one compensator(s) which is mounted to rotate about the locus of a beam of electromagnetic radiation caused to pass therethrough, be selected from the group consisting of:
a single element compensator;
a compensator system comprised of at least two per se. zero-order waveplates, said per se. zero-order waveplates having their respective fast axes rotated to a position offset from zero or ninety degrees with respect to one another, with a nominal value being forty-five degrees;
a compensator system comprised of a combination of at least a first and a second effective zero-order wave plate, said first effective zero-order wave plate being comprised of two multiple order waveplates which are combined with the fast axes thereof oriented at a nominal ninety degrees to one another, and said second effective zero-order wave plate being comprised of two multiple order waveplates which are combined with the fast axes thereof oriented at a nominal ninety degrees to one another; the fast axes and of the multiple order waveplates in said second effective zero-order wave plate being rotated to a position at a nominal forty-five degrees to the fast axes, respectively, of the multiple order waveplates in said first effective zero-order waveplate;
a compensator system comprised of a combination of at least a first and a second effective zero-order wave plate, said first effective zero-order wave plate being comprised of two multiple order waveplates which are combined with the fast axes thereof oriented at a nominal ninety degrees to one another, and said second effective zero-order wave plate being comprised of two multiple order waveplates which are combined with the fast axes thereof oriented at a nominal ninety degrees to one another; the fast axes of the multiple order waveplates in said second effective zero-order wave plate being rotated to a position away from zero or ninety degrees with respect to the fast axes, respectively, of the multiple order waveplates in said first effective zero-order waveplate;
a compensator system comprised of at least one zero-order waveplate, and at least one effective zero-order waveplate, said effective zero-order wave plate, being comprised of two multiple order waveplates which are combined with the fast axes thereof oriented at a nominal ninety degrees to one another, the fast axes of the multiple order waveplates in said effective zero-order wave plate, being rotated to a position away from zero or ninety degrees with respect to the fast axis of the zero-order waveplate;
as are shown in FIGS. 5a-5e. 
Additional compensator systems, as shown in FIGS. 5f-5m, which were previously disclosed in patent application Ser. No. 08/997,311, (now U.S. Pat. No. 5,946,098), and CIP""s therefrom, and which are specifically within the scope of the invention and can be included in the selection group are:
a compensator system comprised of a first triangular shaped element, which as viewed in side elevation presents with first and second sides which project to the left and right and downward from an upper point, which first triangular shaped element first and second sides have reflective outer surfaces; said retarder system further comprising a second triangular shaped element which as viewed in side elevation presents with first and second sides which project to the left and right and downward from an upper point, said second triangular shaped element being made of material which provides reflective interfaces on first and second sides inside thereof; said second triangular shaped element being oriented with respect to the first triangular shaped element such that the upper point of said second triangular shaped element is oriented essentially vertically directly above the upper point of said first triangular shaped element; such that in use an input electromagnetic beam of radiation caused to approach one of said first and second sides of said first triangular shaped element along an essentially horizontally oriented locus, is caused to externally reflect from an outer surface thereof and travel along a locus which is essentially upwardly vertically oriented, then enter said second triangular shaped element and essentially totally internally reflect from one of said first and second sides thereof, then proceed along an essentially horizontal locus and essentially totally internally reflect from the other of said first and second sides and proceed along an essentially downward vertically oriented locus, then externally reflect from the other of said first and second sides of said first triangular shaped elements and proceed along an essentially horizontally oriented locus which is undeviated and undisplaced from the essentially horizontally oriented locus of said input beam of essentially horizontally oriented electromagnetic radiation even when said retarder is caused to rotate; with a result being that retardation is entered between orthogonal components of said input electromagnetic beam of radiation;
a compensator system comprised of, as viewed in upright side elevation, first and second orientation adjustable mirrored elements which each have reflective surfaces; said compensator/retarder system further comprising a third element which, as viewed in upright side elevation, presents with first and second sides which project to the left and right and downward from an upper point, said third element being made of material which provides reflective interfaces on first and second sides inside thereof; said third element being oriented with respect to said first and second orientation adjustable mirrored elements such that in use an input electromagnetic beam of radiation caused to approach one of said first and second orientation adjustable mirrored elements along an essentially horizontally oriented locus, is caused to externally reflect therefrom and travel along a locus which is essentially upwardly vertically oriented, then enter said third element and essentially totally internally reflect from one of said first and second sides thereof, then proceed along an essentially horizontal locus and essentially totally internally reflect from the other of said first and second sides and proceed along an essentially downward vertically oriented locus, then reflect from the other of said first and second orientation adjustable mirrored elements and proceed along an essentially horizontally oriented propagation direction locus which is essentially undeviated and undisplaced from the essentially horizontally oriented propagation direction locus of said input beam of essentially horizontally oriented electromagnetic radiation even when said compensator/retarder is caused to rotate; with a result being that retardation is entered between orthogonal components of said input electromagnetic beam of radiation;
a compensator system comprised of a parallelogram shaped element which, as viewed in side elevation, has top and bottom sides parallel to one another, both said top and bottom sides being oriented essentially horizontally, said retarder system also having right and left sides parallel to one another, both said right and left sides being oriented at an angle to horizontal, said retarder being made of a material with an index of refraction greater than that of a surrounding ambient; such that in use an input beam of electromagnetic radiation caused to enter a side of said retarder selected from the group consisting of: (right and left), along an essentially horizontally oriented locus, is caused to diffracted inside said retarder system and follow a locus which causes it to essentially totally internally reflect from internal interfaces of both said top and bottom sides, and emerge from said retarder system from a side selected from the group consisting of (left and right respectively), along an essentially horizontally oriented locus which is undeviated and undisplaced from the essentially horizontally oriented locus of said input beam of essentially horizontally oriented electromagnetic radiation even when said retarder is caused to rotate; with a result being that retardation is entered between orthogonal components of said input electromagnetic beam of radiation;
a compensator system comprised of first and second triangular shaped elements, said first triangular shaped element, as viewed in side elevation, presenting with first and second sides which project to the left and right and downward from an upper point, said first triangular shaped element further comprising a third side which is oriented essentially horizontally and which is continuous with, and present below said first and second sides; and said second triangular shaped element, as viewed in side elevation, presenting with first and second sides which project to the left and right and upward from an upper point, said second triangular shaped element further comprising a third side which is oriented essentially horizontally and which is continuous with, and present above said first and second sides; said first and second triangular shaped elements being positioned so that a rightmost side of one of said first and second triangular shaped elements is in contact with a leftmost side of the other of said first and second triangular shaped elements over at least a portion of the lengths thereof; said first and second triangular shaped elements each being made of material with an index of refraction greater than that of a surrounding ambient; such that in use an input beam of electromagnetic radiation caused to enter a side of a triangular shaped element selected from the group consisting of: (first and second), not in contact with said other triangular shape element, is caused to diffracted inside said retarder and follow a locus which causes it to essentially totally internally reflect from internal interfaces of said third sides of each of said first and second triangular shaped elements, and emerge from a side of said triangular shaped element selected from the group consisting of: (second and first), not in contact with said other triangular shape element, along an essentially horizontally oriented locus which is undeviated and undisplaced from the essentially horizontally oriented locus of said input beam of essentially horizontally oriented electromagnetic radiation even when said retarder is caused to rotate; with a result being that retardation is entered between orthogonal components of said input electromagnetic beam of radiation;
a compensator system comprised of a triangular shaped element, which as viewed in side elevation presents with first and second sides which project to the left and right and downward from an upper point, said retarder system further comprising a third side which is oriented essentially horizontally and which is continuous with, and present below said first and second sides; said retarder system being made of a material with an index of refraction greater than that of a surrounding ambient; such that in use a an input beam of electromagnetic radiation caused to enter a side of said retarder system selected from the group consisting of: (first and second), along an essentially horizontally oriented locus, is caused to diffracted inside said retarder system and follow a locus which causes it to essentially totally internally reflect from internal interface of said third sides, and emerge from said retarder from a side selected from the group consisting of (second and first respectively), along an essentially horizontally oriented locus which is undeviated and undisplaced from the essentially horizontally oriented locus of said input beam of essentially horizontally oriented electromagnetic radiation even when said retarder system is caused to rotate; with a result being that retardation is entered between orthogonal components of said input electromagnetic beam of radiation; and
a compensator system comprised of first and second Berek-type retarders which each have an optical axes essentially perpendicular to a surface thereof, each of which first and second Berek-type retarders has a fast axis, said fast axes in said first and second Berek-type retarders being oriented in an orientation selected from the group consisting of: (parallel to one another and other than parallel to one another); said first and second Berek-type retarders each presenting with first and second essentially parallel sides, and said first and second Berek-type retarders being oriented, as viewed in side elevation, with first and second sides of one Berek-type retarder being oriented other than parallel to first and second sides of the other Berek-type retarder; such that in use an incident beam of electromagnetic radiation is caused to impinge upon one of said first and second Berek-type retarders on one side thereof, partially transmit therethrough then impinge upon the second Berek-type retarder, on one side thereof, and partially transmit therethrough such that a polarized beam of electromagnetic radiation passing through both of said first and second Berek-type retarders emerges from the second thereof in a polarized state with a phase angle between orthogonal components therein which is different than that in the incident beam of electromagnetic radiation, and in a propagation direction which is essentially undeviated and undisplaced from the incident beam of electromagnetic radiation even when said retarder system is caused to rotate; with a result being that retardation is entered between orthogonal components of said input electromagnetic beam of radiation;
a compensator system comprised of first and second Berek-type retarders which each have an optical axes essentially perpendicular to a surface thereof, each of which first and second Berek-type retarders has a fast axis, said fast axes in said first and second Berek-type retarders being oriented other than parallel to one another; said first and second Berek-type retarders each presenting with first and second essentially parallel sides, and said first and second Berek-type retarders being oriented, as viewed in side elevation, with first and second sides of one Berek-type retarder being oriented other than parallel to first and second sides of the other Berek-type retarder; such that in use an incident beam of electromagnetic radiation is caused to impinge upon one of said first and second Berek-type retarders on one side thereof, partially transmit therethrough then impinge upon the second Berek-type retarder, on one side thereof, and partially transmit therethrough such that a polarized beam of electromagnetic radiation passing through both of said first and second Berek-type retarders emerges from the second thereof in a polarized state with a phase angle between orthogonal components therein which is different than that in the incident beam of electromagnetic radiation, and in a propagation direction which is essentially undeviated and undisplaced from the incident beam of electromagnetic radiation, said spectroscopic ellipsometer/polarimeter system further comprising third and fourth Berek-type retarders which each have an optical axes essentially perpendicular to a surface thereof, each of which third and fourth Berek-type retarders has a fast axis, said fast axes in said third and fourth Berek-type retarders being oriented other than parallel to one another, said third and fourth Berek-type retarders each presenting with first and second essentially parallel sides, and said third and fourth Berek-type retarders being oriented, as viewed in side elevation, with first and second sides of one of said third and fourth Berek-type retarders being oriented other than parallel to first and second sides of said fourth Berek-type retarder; such that in use an incident beam of electromagnetic radiation exiting said second Berek-type retarder is caused to impinge upon said third Berek-type retarder on one side thereof, partially transmit therethrough then impinge upon said fourth Berek-type retarder on one side thereof, and partially transmit therethrough such that a polarized beam of electromagnetic radiation passing through said first, second, third and fourth Berek-type retarders emerges from the fourth thereof in a polarized state with a phase angle between orthogonal components therein which is different than that in the incident beam of electromagnetic radiation caused to impinge upon the first side of said first Berek-type retarder, and in a direction which is essentially undeviated and undisplaced from said incident beam of electromagnetic radiation even when said retarder system is caused to rotate; with a result being that retardation is entered between orthogonal components of said input electromagnetic beam of radiation;
a compensator system comprised of first, second, third and fourth Berek-type retarders which each have an optical axes essentially perpendicular to a surface thereof, each of which first and second Berek-type retarders has a fast axis, said fast axes in said first and second Berek-type retarders being oriented essentially parallel to one another; said first and second Berek-type retarders each presenting with first and second essentially parallel sides, and said first and second Berek-type retarders being oriented, as viewed in side elevation, with first and second sides of one Berek-type retarder being oriented other than parallel to first and second sides of the other Berek-type retarder; such that in use an incident beam of electromagnetic radiation is caused to impinge upon one of said first and second Berek-type retarders on one side thereof, partially transmit therethrough then impinge upon the second Berek-type retarder, on one side thereof, and partially transmit therethrough such that a polarized beam of electromagnetic radiation passing through both of said first and second Berek-type retarders emerges from the second thereof in a polarized state with a phase angle between orthogonal components therein which is different than that in the incident beam of electromagnetic radiation, and in a propagation direction which is essentially undeviated and undisplaced from the incident beam of electromagnetic radiation; each of which third and fourth Berek-type retarders has a fast axis, said fast axes in said third and fourth Berek-type retarders being oriented essentially parallel to one another but other than parallel to the fast axes of said first and second Berek-type retarders, said third and fourth Berek-type retarders each presenting with first and second essentially parallel sides, and said third and fourth Berek-type retarders being oriented, as viewed in side elevation, with first and second sides of one of said third and fourth Berek-type retarders being oriented other than parallel to first and second sides of said fourth Berek-type retarder; such that in use an incident beam of electromagnetic radiation exiting said second Berek-type retarder is caused to impinge upon said third Berek-type retarder on one side thereof, partially transmit therethrough then impinge upon said fourth Berek-type retarder on one side thereof, and partially transmit therethrough such that a polarized beam of electromagnetic radiation passing through said first, second, third and fourth Berek-type retarders emerges from the fourth thereof in a polarized state with a phase angle between orthogonal components therein which is different than that in the incident beam of electromagnetic radiation caused to impinge upon the first side of said first Berek-type retarder, and in a direction which is essentially undeviated and undisplaced from said incident beam of electromagnetic radiation even when said retarder system is caused to rotate; with a result being that retardation is entered between orthogonal components of said input electromagnetic beam of radiation.
A present invention spectroscopic rotatable compensator ellipsometer system can also comprise at least one compensator(s) which produces a retardance of, preferably, between seventy-five (75) and one-hundred-thirty (130) degrees over a range of wavelengths defined by a selection from the group consisting of:
a. between one-hundred-ninety (190) and seven-hundred-fifty (750) nanometers;
b. between two-hundred-forty-five (245) and nine-hundred (900) nanometers;
c. between three-hundred-eighty (380) and seventeen-hundred (1700) nanometers;
d. within a range of wavelengths defined by a maximum wavelength (MAXW) and a minimum wavelength (MINW) wherein the ratio of (MAXW)/(MINW) is at least one-and-eight-tenths (1.8).
Acceptable practice however, also provides for the case wherein at least one of said at least one compensator(s) provides a retardation vs. wavelength characteristic retardation between thirty (30.0) and less than one-hundred-thirty-five (135) degrees over a range of wavelengths specified from MINW to MAXW by a selection from the group consisting of:
a. MINW less than/equal to one-hundred-ninety (190) and MAXW greater than/equal to seventeen-hundred (1700);
b. MINW less than/equal to two-hundred-twenty (220) and MAXW greater than/equal to one-thousand (1000) nanometers;
c. within a range of wavelengths defined by a maximum wavelength (MAXW) and a minimum wavelength (MINW) range where (MAXW)/(MINW) is at least four-and one-half (4.5).
(NOTE, the specified vales and ranges can not be achieved by single plates with (1/wavelength) retardation characteristics).
The present invention will be better understood by reference to the Detailed Description Section of this Disclosure, in conjunction with the accompanying Drawings.
It is therefore a purpose and/or objective of the present invention to provide, in the context of a rotating compensator ellipsometer sytem, a spatial filter system and method for forming a beam of electromagnetic radiation which presents with an intensity profile which radially drops off quickly to zero (0.0) without demonstrating low level oscillations similar to Fourier Transform of a Square Wave characteristics.
It is another purpose and/or objective of the present invention to teach, either prior to or after a sample system, application of a spatial filter system for forming a beam of electromagnetic radiation which, for instance, presents with an intensity profile which drops off quickly to zero (0.0), in spectroscopic rotating compensator ellipsometer systems.
Other purposes and/or objectives of the present invention will become obvious from a reading of the Specification and Claims.